Demon ninja

While most ninja were human, some demons were able to master the ninjustu art as well, and their techniques, powered by yōki were far more formidable than a normal ninja. Their leader, and the most powerful demon ninja of all, was Hoshiyomi.

The ninjas who served under Hoshiyomi are named after the four legendary creatures in Chinese mythology that guard the four cardinal directions on the compass. There's also another group called the Shitōshin who follow the same trope.